1. Field of the Invention
The present invention relates to downhole telemetry systems, and more particularly to wired conduit such as drill pipe that is adapted for conveying data and/or power between one or more downhole locations within a borehole and the surface.
2. Background of the Related Art
Measurement While Drilling (MWD) and Logging While Drilling (LWD) systems derive much of their value from the ability to provide real-time information about downhole conditions near the drill bit. Oil companies use these downhole measurements to make decisions during the drilling process, e.g., to provide input or feedback information for sophisticated drilling techniques such as the GeoSteering system developed by Schlumberger. Such techniques rely heavily on instantaneous knowledge of the formation that is being drilled. Accordingly, the industry continues to develop new real-time (or near real-time) measurements for MWD/LWD, including imaging-type measurements with high data content.
Such new measurements and the related control systems require telemetry systems having higher data transmission rates than those currently available. As a result, a number of new and/or modified telemetry techniques for use with MWD/LWD systems have been proposed or tried with varying degrees of success.
The conventional industry standard for data transmission between downhole and surface locations is mud-pulse telemetry wherein the drill string is used to convey modulated acoustic waves in the drilling fluid. Data transmission rates using mud-pulse telemetry lie in the range of 1-6 bits/second. Such slow rates are incapable of transmitting the large amounts of data that are typically gathered with an LWD string. Additionally, in some cases (e.g., when using foamed drilling fluid), mud-pulse telemetry does not work at all. As a result, it is not uncommon for some or all of the data collected by MWD/LWD systems to be stored in downhole memory and downloaded at the end of a bit run. This delay significantly reduces the value of the data for real-time or near real-time applications. Also, there is a significant risk of data loss, for example, if the MWD/LWD tool(s) are lost in the borehole.
Electromagnetic (EM) telemetry via subsurface earth pathways has been tried with limited success. The utility of EM telemetry is also depth-limited, depending on the resistivity of the earth, even at low data transmission rates.
Acoustic telemetry through the drill pipe itself has been studied extensively but has not been used commercially to date. In theory, data transmission rates in the 10's of bits/second should be possible using acoustic waves conveyed through the steel drill string, but this has not been reliably proven.
The concept of routing a wire in interconnected drill pipe joints has been proposed numerous times over the past 25 years. Some of the prior proposals are disclosed in: U.S. Pat. No. 4,126,848 by Denison; U.S. Pat. No. 3,957,118 by Barry et al.; and U.S. Pat. No. 3,807,502 by Heilhecker et al.; and in publications such as “Four Different Systems Used for MWD”, W. J. McDonald, The Oil and Gas Journal, pages 115-124, Apr. 3, 1978.
A number of more recent patents and publication have focused on the use of current-coupled inductive couplers in wired drill pipe (WDP). U.S. Pat. No. 4,605,268 by Meador describes the use and basic operation of current-coupled inductive couplers mounted at the sealing faces of drill pipes. Russian Federation published Patent Application No. 2140537 by Basarygin et al., and an earlier Russian Federation published Patent Application No. 2040691 by Konovalov et al., both describe a drill pipe telemetry system that uses current-coupled inductive couplers mounted proximate to the sealing faces of drill pipes. International Publication No. WO 90/14497 A2 by Jürgens et al. describes an inductive coupler mounted at the ID of the drill pipe joint for data transfer. Other relevant patents include the following U.S. Pat. No. 5,052,941 by Hernandez-Marti et al.; U.S. Pat. No. 4,806,928 by Veneruso; U.S. Pat. No. 4,901,069 by Veneruso; U.S. Pat. No. 5,531,592 by Veneruso; U.S. Pat. No. 5,278,550 by Rhein-Knudsen, et al.; U.S. Pat. No. 5,971,072 by Huber et al.; and U.S. Pat. No. 6,641,434 by Boyle et al.
The above references are generally focused on the transmission of data across the coupled ends of interconnected drill pipe joints, rather than along the axial lengths of the pipe joints. A number of other patent references have disclosed or suggested particular solutions for data transmission along the axial lengths of downhole conduit or pipe joints, including: U.S. Pat. No. 2,000,716 by Polk; U.S. Pat. No. 2,096,359 by Hawthorn; U.S. Pat. No. 4,095,865 by Denison et al.; U.S. Pat. No. 4,72,402 by Weldon; U.S. Pat. No. 4,953,636 by Mohn; U.S. Pat. No. 6,392,317 by Hall et al.; and U.S. Pat. No. 6,799,632 by Hall et al. Other relevant patent references include International Publication No. WO 2004/033847 A1 by Williams et al., International Publication No. WO 0206716 A1 by Hall et al., and U.S. Publication No. US 2004/0119607 A1 by Davies et al.